feat: add support for plex new nfo agent

[arabcoders]

This PR adds support for Plex's native NFO agents, allowing WatchState to recognize and import libraries using the new Plex NFO movie and series agents.

The new supported agents are:

• tv.plex.agents.nfo.movie
• tv.plex.agents.nfo.series

WatchState now treats these as supported Plex agents, parses their typed GUIDs, and normalizes provider-backed IDs such as tmdb_383498, imdb_tt1234567, and tvdb_121361 into the same canonical external IDs used by the rest of the application.

Changes

• Added support for Plex native NFO movie and series agents.
• Added GUID parsing for typed Plex NFO identifiers such as:
  • tv.plex.agents.nfo.movie://movie/tmdb_383498
  • tv.plex.agents.nfo.movie://movie/imdb_tt1234567
  • tv.plex.agents.nfo.series://show/tvdb_121361
• Ensured untyped/fallback NFO IDs that do not expose a provider are ignored instead of being guessed.
• Updated Plex library detection so NFO-backed movie and show libraries are marked as supported.
• Updated Plex import and entity conversion tests to cover NFO-backed libraries, movies, shows, and episodes.
• Updated the FAQ with the new Plex NFO GUID formats and cleaned up the legacy agent list.

Minor changes

• Added a bundled OpenAPI viewer under Help for browsing Plex, Jellyfin, and Emby upstream routes.
• Added static serving for bundled backend OpenAPI JSON files.
• Improved log formatting so event logs expose timestamps, history item links, user/backend metadata, and handle non-string payloads safely.
• Improved frontend log rendering with timestamp display, history item navigation, filtering, and copy behavior.
• Fixed navigation active-state handling for nested Help pages such as API, OpenAPI, README, FAQ, and News.
• Changed backend library ignore toggling to update the backend ignore option list directly.
• Refactored state import request handling to run through the adapter-managed transaction path.
• Fixed SQLite prepared statement reuse issues, including null/scalar binding and retry handling for 21 bad parameter or other API misuse.